[Kea-users] DHCP4 MySQL Host Reservation Troubles

[Bryan Perry]

Thank You Marcin.

You have understood exactly my problem, and it's worth noting that 3 
subnets is only the beginning. Ultimately there will be upwards of 30 
subnets, with 2 or 3 being dedicated to static clients. This would be 30 
reservations stored and managed for each of several hundred clients. 
That would get unruly very quickly.

It seems like Kea should check for reservations before assigning a 
subnet in order to avoid this problem, but there may be another way 
around this.

If I use the subnet4_select hook to intercept the request, check the 
database for reservations in a callout function, modify the assigned 
subnet and send the data back from the callout, then Kea should be able 
to process the request using the subnet ID associated with the 
reservation. I posted a few minutes ago asking for a code example of how 
to do the modification of the subnet ID.

That's the only solution I could come up with to work around this 
limitation. Did I miss another or better option?

And really, Thanks for the help.
Bryan

On 5/12/2016 11:27 AM, Marcin Siodelski wrote:
> Hi Bryan,
>
> Let me summarize your issue, so as we check if I understand it correctly:
>
> - You have 3 subnets where you have DHCP clients, of which some have and
> some don't have static reservations.
> - Router (relay agent) will use one of 3 different giaddrs when relaying
> messages to the server over a single link (relay-server link) connected
> to a particular interface on the DHCP server.
> - For clients for which addresses should be assigned dynamically we want
> the server to use giaddr to pick the correct subnet.
> - For other clients, which have static addresses, it is possible that
> the giaddr may vary and in 2 out of 3 cases the client will not have a
> subnet corresponding to his static reservation selected. As a result the
> client will get a dynamically assigned address, rather than static one.
> - You want to define a static reservation for a given client's MAC
> address which should be used regardless of the giaddr appearing in a
> relayed message.
>
> The problem with this approach is that our host reservations are
> strictly associated with a subnet (subnet id) selected for a client.
> This selection takes place even before we check for host reservations.
> The subnet id (and MAC address) is used as an input to search for static
> reservations for a client.
>
> I need to think a bit more about this issue, but for a time being, would
> it be simply possible to insert 3 reservations for the same host,
> differing by the subnet identifier? In that case, no matter which subnet
> id is selected for the client, the server should always find a suitable
> reservation. That may be not viable if I misunderstood your use case :-).
>
> This also has an issue that you have redundant information in the
> database and this doesn't scale well with many reservations.
>
> Thanks,
> Marcin Siodelski
> ISC
>
> On 11.05.2016 23:24, Bryan Perry wrote:
>> So any guidance from the ISC gurus on this topic? My host reservation
>> seems to work fine only if the correct subnet is assigned, but if a
>> different subnet (still part of the same shared network) is assigned
>> then the client gets a lease from a pool. If I lock down the upstream
>> router to only use the XXX.YYY.169.1 giaddr then normal DHCP clients who
>> need addresses from the 170 or 171 subnets get nothing.
>>
>> Can I define multiple non-contiguous address pools inside the same
>> subnet declaration to handle both the static and dynamic clients?
>>
>> I'm stumped. Thanks for any help.
>> -Bryan
>>
>> On 5/10/2016 1:05 PM, Thomas Andersen wrote:
>>> Not sure that you can, and I’m not sure it’s how it is intended.
>>> But it’s a bit deeper than what i normally deal with.
>>>
>>> Maybe one of the ISC guys can elaborate.
>>>
>>>
>>> Br,
>>> Thomas
>>>
>>>
>>>
>>>
>>> On 10/05/16 20:58, "kea-users-bounces at lists.isc.org on behalf of Bryan
>>> Perry" <kea-users-bounces at lists.isc.org on behalf of bryan at sfcn.org>
>>> wrote:
>>>
>>>> So the question becomes, how do I force it back to subnet 169 when the
>>>> DHCPDISCOVER comes in from the .170.1 relay address (which is the same
>>>> router) and the hosts entry is for subnet 169?
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>
>